The objective of the proposed research is to elucidate the role of matrix vesicles in the initiation and regulation of biological calcification. Effort is being made to characterize matrix vesicles with regard to their content and metabolism of calcium and phosphate, enzymes, lipids, and other proteins. Special emphasis is being placed on the role of alkaline phoshatase, phospholipases, prostaglandins, and acidic phospholipic-calcium phosphate complexes in the de novo formation and regulation of mineral deposition by matrix vesicles.